owl.Restriction(property,graph=graph,cardinality=Literal(0)) Raises an error.
assert len(validRestrProps)
When cardinality value is given as 0.

This comes from:

  validRestrProps = [(i, oTerm) for (i, oTerm) in restrTypes if i]
  assert len(validRestrProps)

I believe this is an oversight as if i == 0 returns False.
However, I believe cardinality: 0 is valid.